OBJECTIVES: We will continue the resolution of all of the rat liver microsomal enzymes, electron carriers, and supporting lipids and non-catalytic proteins of cholesterol biosynthesis from lanosterol. When each purified component is obtained reconstitution studies will be carried out ultimately to achieve complete enzymic synthesis of cholesterol from lanosterol with purified components. We will continue the study of concerted regulation of the activities of the microsomal enzymes including HMG-CoA reductase. Each of the noncatalytic proteins associated with regulation will be purified and characterized physically and functionally. Studies will be carried out with microsomes from liver, solid tumors, and hepatocyte and hepatoma cells in culture. The role of microsomal electron transport in eleven of the terminal 20 reactions of cholesterol biosynthesis will be described further by carrying out reconstitution experiments. Cytochrome P-450-dependent methyl sterol oxidases will be studied first. Electron transport to biosynthetic oxidases will be contrasted to the much more-studied xenobiotic oxidases. The multienzymic nature of these enzymes will be studied by investigating a) the associations of the enzymes and ancillary proteins with the membrane, b) the roles of lipids in the membrane, and c) the associations of the enzymes and ancillary proteins with each other.